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Frisky flower uses bellows to blast pollen at birds

By Shreya Dasgupta

Video: Frisky flower uses bellows to blast pollen at birds

The bulbous male parts of Axinaea

(Image: Current Biology, Dellinger et al.)

For one group of plants, having brightly coloured flowers isn’t enough to guarantee being pollinated. When birds rip bits out of the flowers to eat them, special bellow-like organs blast pollen onto their feathers.

The male parts of flowers produce pollen, which insects and birds pick up and carry to the female parts, either of the same flower or a different one, as they dive into flowers in search of nectar or pollen. Normally this is a passive process on the part of the plants&colon; the animal must rummage around in the flower to pick up the pollen. But the colourful flowers in plants of the Axinaea genus take matters into their own hands, perhaps because birds tend to eat the pollen-covered male parts in their entirety.

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When a bird grabs one of the bulbous stamens that sit inside an Axinaeaflower, this male organ explodes, spraying a messy jet of pollen onto the bird’s beak, face and neck (see video, above). As the bird feeds, brushing past various parts of the flower as it grabs the next mouthful, the pollen gets dusted onto the female reproductive organs.

Jürg Schönenberger of the University of Vienna in Austria and his colleagues observed and videoed pollinators visiting Axinaea in Ecuador and Costa Rica. They also analysed the flowers’ stamen structures and their contents.

Squirt of pollen

Most other plants of the Melastomataceae family, to which Axinaea belongs, are pollinated by bees, whose vibrating flight muscles cause anthers to expel pollen. But Axinaea anthers work like paper bags full of air. “If you press the bag, the air flushes into the pollen chamber and then out through a pore at the other end of the anther of the stamen, blasting pollen at the birds,” says Schönenberger.

The birds visit the flowers because the bulbous stamens reward them with a rich, sugary concoction. “I was surprised that the yellow food bodies on the male parts of these flowers contain so much sugar,” says Susanne Renner of the Ludwig Maximilian University of Munich in Germany. “Birds feed on them as if they were berries. I just assumed that bees would visit the flowers to collect pollen.”

The birds completely eat the stamens and all its pollen, which makes it more difficult for the female parts of the plant to get pollinated. The bellow mechanism may ensure that the pollen gets onto the bird quickly, before the bird eats the flower’s entire male reproductive organ, says Schönenberger.

“These specialised bellow organs simultaneously serve as food sources and pollen placement machinery,” says Stacey Smith of the University of Colorado in Boulder.

It’s not clear why Axinaea switched from bee pollination to bird pollination. But Schönenberger says it may be because Axinaea live at high altitudes, where bees are less common.